EP2106297B1

EP2106297B1 - Device and method for separating a flowing medium mixture with a stationary cyclone

Info

Publication number: EP2106297B1
Application number: EP08705081A
Authority: EP
Inventors: Robert Schook
Original assignee: TAXON BV
Current assignee: Sulzer Chemtech AG
Priority date: 2007-01-11
Filing date: 2008-01-08
Publication date: 2012-09-12
Anticipated expiration: 2028-01-08
Also published as: US8343360B2; EP2106297A1; DK2106297T4; WO2008085042A1; NL2000429C2; ES2398304T3; ES2398304T5; MY149617A; CA2675163C; US20100140187A1; EP2106297B2; DK2106297T3; BRPI0806209B1; BRPI0806209A2; CA2675163A1

Description

The invention relates to a device for separating a flowing medium mixture into at least two different fractions with differing average mass density as according to the preamble of claim 1. Such a device is also referred to as a stationary cyclone. The invention also relates to a method for separating a flowing medium mixture into at least two fractions of differing mass density using such a stationary cyclone according the preamble of claim 10.
The separation of a flowing medium mixture has very diverse applications. Medium mixture is here understood to mean a mixture of at least one liquid or a gas which can be mixed with solid material parts such as a powder or an aerosol. Examples are a gas/gas mixture, a gas/liquid mixture, a liquid/liquid mixture, a gas/solid mixture, a liquid/solid mixture, or any of the said mixtures provided with one or more additional fractions. The separation of a flowing medium mixture is for instance known from various applications of liquid cleaning, (flue) gas cleaning and powder separation. Separation of fractions with a great difference in particle size and/or a great difference in mass density is relatively simple. Large-scale use is made for this purpose of processes such as filtration and screening. In the separation of fractions with a smaller difference in mass density use is made of chemical separating techniques and/or separating techniques such as sedimentation and centrifugation. A relatively simple and therefore inexpensive technology, with which large volumes can be separated in line, makes use of the differences in mass density of the fractions for separating by applying a centripetal force to the mixture by means of rotating the mixture in for instance a centrifuge or a cyclone. A relatively simple separating device, which consists of a stationary housing in which a vortex, i.e. a rotating mixture, can be generated, is for instance described in WO 97/05956 and WO 97/28903 . The devices shown here are also referred to as "hydrocyclones" and are particularly suitable for liquid/liquid separation. It is noted that the fractions obtained after separation can still have ("be contaminated with") a part of the other fraction even after separation, although the fractions both have a composition clearly differing from the composition of the original mixture.
The French patent application FR 2134520 describes a cyclone comprising a first feed part connecting radially to the separating space. The cyclone is also provided with a throughfeed part which allows passage of the mixture in lateral direction and to which connects a guide with curved guide elements, whereby a radial flow direction is obtained. Once the mixture has been set into rotating movement it is carried through a separator tube. Use of this construction will at best result in a mediocre separating result.
US patent 3,535,850 discloses a centrifugal particle separator for processing dust-laden air under atmospheric pressure that comprises an elongated cylindrical housing forming a vortex chamber with a swirl or spin component to generate a natural vortex flow within the vortex chamber. The feed of the dust-laden air leads radially inward and as a result of the rotation of the dust-laden air in the stationary housing of the cyclone a lighter fraction will at least substantially migrate to the inner side of the vortex and the heavier dust fraction will migrate to the outer side of the vortex. The air fraction and the dust fraction are discharged at spaced apart positions from the cyclone; the dust fraction at a point radially outward of the vortex.
US patent 6,702,877 is considered to represent the closest prior art and discloses a device for separating a mixture of gas with liquid and/or solid which comprises a gravity separation vessel and a processing vessel which can be mounted in the separation vessel. The mixture to be separated is fed from one side horizontally (arrow B) to an upper inlet chamber from where the mixture flows downwards in adjacent cyclones. Subsequently swirling blades make the mixture set into rotation into the cyclones. The heavy fraction of the mixture flows down and out the cyclones through conical taperings while the light fraction is discharged on the upper side of the cyclones
The present invention has for its object, with limited investment, to increase the efficiency and/or the effectiveness of the separation of fractions of a flowing medium mixture using a vortex generated in a stationary housing.
The invention provides for this purpose a device as according to claim 1. The separating space usually has an elongate form having an inner side of circular cross-section (i.e. a cross-section perpendicularly of the longitudinal direction or lengthwise axis of the cyclone). The separating space can be provided as desired with a core around which the mixture is set into rotation as a vortex. The device according to the invention is provided with a plurality of first feed parts which connect to the separating space from different radial directions, preferably such that the plurality of first feed parts connect at equal mutual angles to the periphery of the separating space. In other words, this means that they connect at equal mutual distances to the periphery of the generally circular outer wall of the separating space. Advantageous results have been achieved in practice with twelve (12) first feed parts distributed evenly over the periphery. This provides for a uniform inflow of the mixture for separating such that a stable flow pattern occurs in the separating space sooner than if the device is only provided with one or a few first feed parts according the prior art. A stable flow pattern has the advantage that the (pre)separation already present in the mixture is sustained. The pre-separation resulting from the inflow will be further elucidated below; in combination with the multiple feed the obtained pre-separation will be maintained. Owing to the rotation means the flow direction changes in axial direction of the device from axial to tangential (V becomes greater in axial direction). Said measures will in combination therefore result in an unexpected increase in the separating capacity of the device. This is further enhanced when the first feed parts connect at mutually equal angles to the periphery of the separating space.
The separation thus takes place not only in the separating space, but the mixture for separating enters the separating space in an already pre-separated state (i.e. a state in which it is no longer possible to speak of a homogenous mixture), i.e. in a state in which an already partial separation has taken place. This pre-separation is obtained during the feed of the mixture for separating by creating a transition from the initial radial feed direction to the final feed direction in which the mixture is fed to the separating space substantially tangentially of the inner wall of the separating space (i.e. parallel to the orientation of the inner wall at the position of the actual connection to the vortex) and by also maintaining this pre-separation of the mixture. As a result of the changing flow direction in the feed path a heavier and a lighter fraction of the mixture for separating have different preferred flow directions; a heavier fraction has a greater preference for maintaining an existing flow direction than a lighter fraction. This is because heavier particles have a greater mass inertia, and will therefore be less inclined to follow a change in the flow direction than lighter particles. A first degree of separation (pre-separation) is thus already obtained during feed. Now that measures are also taken so that this pre-separation is not lost on the subsequent inflow path into the separation space, it is possible using a vortex which remains constant to obtain an increased measure of separation or to suffice with a shorter retention time of, or a reduced pressure drop over, the mixture in the cyclone so as to obtain an identical degree of separation as with the prior art cyclones.
A further advantage of the device according to the present invention is that the device can be given a very compact form, among other reasons because of the multiple feed connecting to the separating space.
In a particular preferred variant the passage area of the separating space decreases in axial direction. The passage area is understood here to mean the area of the separating space in a direction perpendicular to the axial direction. If the axial direction is defined as "Z", this means: dA/dZ < 0. It is noted here that decreasing is particularly understood to mean continuously decreasing, but that - although less desirable - dA/dZ ≤ 0 may also apply locally. The narrowing progression of the separating space is favourable for preventing, among other things, boundary layer separation. This measure thus also contributes toward the further stabilization of the flow so that no deterioration in the already realized (pre-)separation occurs. This condition can for instance be met when the separating space is tapering. If the separating space is provided with an end pipe, it is advantageous that this be conical.
In another advantageous embodiment variant the third feed part comprises curved guide elements, while still further optimization can be realized if a curved stabilizing element is positioned between two adjacent curved guide elements of the third feed part. The difference between the curved guide elements and the curved stabilizing elements consists here of, among others, the difference in length between the two. It is also the case that the curved guide elements locally divide the feed into mutually separate compartments, while this does not have to be the case with the curved stabilizing elements. These are once again measures with which a stable flow pattern can be obtained. The outflow direction of the guide elements is substantially tangential to the inner wall of the separating space. The advantage of giving a stabilizing element a desirably shorter form is that it thus prevents flow blockage. As a result of these measures the local Reynolds number will clearly decrease at different locations in the feed, whereby the chance of heavily turbulent flow in the feed (with a Reynolds number much greater than 2300 evidently being undesirable from a separating viewpoint) becomes considerably smaller, also at a higher flow rate.
The present invention makes it possible for the diameter of the separating space to be smaller than 75, 50, 25 or 10 mm. The diameter of the separating space is more specifically understood to mean the internal diameter of the separating space. This dimensioning is important to the extent that it is possible to manufacture devices of (very) limited size which can fit readily into all kinds of existing production processes and production equipment.
In a particularly practical embodiment variant the device is provided with an assembly of a plurality of feeds as described above combined into a single construction part. The feeds can herein be placed in a circle. A separate third tangential feed part, and optionally also a second axial feed part, can connect to each first radial feed part, although it is also possible for a plurality of first radial feed parts to connect to a shared third tangential feed part, and optionally also to a shared second axial feed part. The transition between successive feed parts, particularly though not exclusively the transition from a first radial feed part to the second axial feed part, can be formed by a channel having at least one curved guide surface. The advantage of the first feed part transposing into the third feed part by means of a curved guide is that this measure also contributes toward the uniform transition from the radial flow direction to another (axial or directly tangential) flow direction. This measure is also advantageous in respect of stabilizing the flow.
In order to also facilitate this transition in flow direction of the medium, the feed can also have between the first radial feed part and the third tangential feed part an intermediate second axial feed part running substantially parallel to the longitudinal axis of the separating space. By means of this measure the number of changes in the flow direction (and/or the retention time for the purpose of pre-separation) increases during feed, which results in an increased measure of pre-separation. This construction moreover enables simple integration of the feed with the separating space.
The invention also relates to a method for separating a flowing medium mixture into at least two fractions with differing mass density as according to claim 10. The directions in which the different supplied fractions are fed to the stationary cyclone here preferably enclose mutually equal angles. The mixture for separating preferably has, between the initial radial flow directions and the final substantially tangential flow direction, a flow direction which is preferably substantially parallel to the longitudinal axis of the cyclone (in axial direction).
It is desirable for the purpose of obtaining an optimum pre-separation that the medium mixture has a substantially laminar flow pattern during processing step A). A substantially laminar flow pattern here also includes the transition zone in which the laminar flow pattern transposes into a (heavily) turbulent flow pattern (with a typical Reynolds number in the order of magnitude of several thousand), more particularly a flow pattern wherein the Reynolds number is smaller than 2300, preferably smaller than 2000, but still more desirably less than respectively 1500, 1200 or 1000. By means of this method the advantages can be realized as already described above with reference to the device according to the invention.
In order to obtain an even better separation result, it can also be advantageous if the medium mixture expands (instantaneously) during the feed over the feed openings, for instance expands such that microbubbles are created. This principle works if the medium mixture is supersaturated upon entry into the cyclone. The microbubbles that are present adhere to the lighter fraction, whereby the effective difference in mass density of the fractions for separating increases.
The present invention will be further elucidated on the basis of the non-limitative exemplary embodiments shown in the following figures. Herein:

figure 1 shows a perspective and partly cut-away view of a separating device according to the invention;
figures 2A and 2B show respectively a perspective view and a side view of a feed element, as this forms part of the separating device shown in figure 1, integrated with a core of a cyclone; and
figure 3 is a side view of the outer side of the separating device shown in figure 1.

Figure 1 shows a separating device 1, also referred to as a static cyclone or hydrocyclone, with a casing 2 in which are arranged a number of feed openings 3 for a medium mixture to be processed. Casing 2 of separating device 1 encloses a separating space having a central axis (or longitudinal axis) 4 relative to which the feed openings 3 are positioned radially. The medium mixture supplied radially through feed openings 3 is urged (axially) substantially in a direction parallel to central axis 4 by curved guide surfaces 5 connecting to feed openings 3. Disposed downstream of these guide surfaces 5 in flow direction are curved guide elements 6 which direct the medium mixture in a more tangential direction relative to casing 2. Shorter stabilizers 7 are placed between guide elements 6, as a result of which a substantially more laminar flow can be maintained, even at higher flow speeds, between guide elements 6 and stabilizers 7.
A core 8 is provided centrally in casing 2. Guide elements 6 and stabilizers 7 connect to both the inner side of casing 2 and core 8 so that all the medium is carried in forced manner between guide elements 6. Guide elements 6 are formed such that they have a sharper curvature at a greater distance from feed openings 3. A discharge opening 9 for the lighter fraction of the mixture is arranged centrally in core 8. Through rotation of the mixture, particularly in the narrowed part 10 of separating device 1, the lighter fraction will be displaced to a position close to central axis 4, whereby it can be removed from separating device 1 through discharge opening 9 in core 8. The heavier fraction of the mixture will migrate in the narrowed part 10 of separating device 1 toward casing 2 and subsequently be discharged from separating device 1 through outlet opening 11. The length 10 can in reality be much greater than the scale with which it is shown here. It is also desirable that dA/dZ < 0 or that dA/dZ ≤ 0 in the area where core 8 is situated.
Figures 2A and 2B show views of core 8 of figure 1 having assembled integrally therewith the guide surfaces 5, guide elements 6 and stabilizers 7. Stabilizers 7 do not necessarily have to be present; separation device 1 will also be able to function without these stabilizers 7. The transition from a radial flow direction to an axially oriented flow takes place in a first zone Z₁ (see figure 2B), while the axially oriented flow is converted to a substantially tangential flow direction in the second zone Z₂ (see figure 2B).
Figure 3 shows separating device 1 to which a medium mixture for separating is fed through feed openings 3 as according to arrows P₁. A heavier fraction will leave separating device 1 on a proximal side as according to arrow P₂, while the lighter fraction will leave separating device 1 on the distal side as according to arrow P₃. The shown separating device 1 is particularly suitable for application as oil/water separator. It will however be apparent that other applications, a different dimensioning and alternative embodiment variants also fall within the scope of protection of the present invention.

Claims

Device (1) for separating a flowing medium mixture into at least two different fractions with differing average mass density, comprising:
- an elongate separating space which is circle-symmetrical in axial direction and enclosed by a stationary casing (2), wherein the casing (2) is provided with a feed (3) for a mixture for separating and at least two discharges (9, 11) for discharging at least two fractions with differing mass density of which the discharge (11) for the heavy fraction is connecting centrally to the separating space, and

- rotation means (6) located in the separating space for causing the mixture to rotate as a vortex in the separating space,
wherein the feed (3) for a mixture for separating initially connects by means of a first feed part to the separating space and transposes (5) into a third feed part (Z₂) which forms the rotation means (6) and debouches substantially tangentially in the separating space,
characterized in that the first feed part connects substantially radially to the stationary casing (2) via a plurality of first feed parts (3) that are arranged as a number of feed openings (3) in the stationary casing (2) and so connect to the separating space from different radial directions.
Device (1) as claimed in claim 1, characterized in that the number of feed openings (3) forming the plurality of first feed parts (3) connect at equal mutual angles to the periphery of the stationary casing (2) of the separating space.
Device (1) as claimed in claim 1 or 2, characterized in that the discharge (11) for the heavy fraction is connecting centrally to a passage area (10) of the separating space that decreases in axial direction.
Device (1) as claimed in any of the foregoing claims, characterized in that the third feed part (Z₂) comprises curved guide elements (6).
Device (1) as claimed in claim 4, characterized in that a curved stabilizing element (7) is positioned between two adjacent curved guide elements (6) of the third feed part (Z₂).
Device (1) as claimed in any of the foregoing claims, characterized in that the diameter of the separating space is smaller than 75, 50, 25 or 10 mm.
Device (1) as claimed in any of the foregoing claims, characterized in that between the first radial feed part and the third tangential feed part (Z₂) the feed has an intermediate second axial feed part running substantially parallel to the longitudinal axis (4) of the separating space.
Device (1) as claimed in any of the foregoing claims, characterized in that the first feed part transposes by means of a curved guide (5) into the third feed part (Z₂).
Device (1) as claimed in any of the claims 4 - 8, characterized in that the curved guide elements (6) of the third feed part (Z₂) connect to feed openings (3) in the stationary casing (2).
Method for separating a flowing medium mixture into at least two fractions with differing mass density, comprising the processing steps of:
A) feeding a mixture for separating to a stationary cyclone according the device (1) as claimed in any of the claims 1 - 9,

B) causing the flowing mixture for separating to rotate as a vortex in a stationary circle-symmetrical, elongate housing (2) of the cyclone, and

C) discharging at least two separated fractions from the housing (2) of the stationary cyclone whereby the heavy fraction is discharged centrally form the housing (2) of the cyclone,
characterized in that the mixture for separating is fed in different fractions from different radial directions to the stationary cyclone during processing step A) via a plurality of first feed parts (3) that are arranged as a number of feed openings (3) in the stationary casing (2).
Method as claimed in claim 10, characterized in that the directions in which the different supplied fractions via a plurality of first feed parts (3) are fed to the stationary cyclone enclose mutually equal angles.
Method as claimed in claim 10 or 11, characterized in that between the initial, substantially radial flow directions and the final substantially tangential flow direction the mixture for separating has an intermediate flow direction during processing step A) which is substantially axial (4) to the vortex.
Method as claimed in any of the claims 10-12, characterized in that the flow of the medium mixture to be fed to the cyclone has a substantially laminar flow pattern during processing step A).
Method as claimed in any of the claims 10-13, characterized in that the medium mixture expands (instantaneously) during the feed to the vortex.